Nonoscillating radiofrequency selective amplifier



Nov. 2:, 1920. 1,605,411

' C. 0. WEBER NONOSCILLATING RADIOFREQUENCY SELECTIVE AMPLIFIER Oriszinal Filed June 6. 1924 vwentoz @Mq sum,

Patented Nov. 2, 1926.

UNITED STATES 1,605,411 PATENT OFFICE.

CARL O. WEBER, OF NEW YORK, N. Y.

NONOSCILLATING RADIOFREQUENCY SELECTIVE AMPLIFIER.

Original application filed June 6, 1924, Serial No. 718,223. Divided and this application filed June 2,

1926. Serial This application is a division of my copending application, Ser. No. 718,223, filed June 6th, 1924, for dynodyne radio rece iving set, and is specific to the combination of a tuning variable condenser connected across the terminals of the secondary coil of an air core radio transformer which secondary coil is spaced from its primary cOil of a smaller number of turns which turns are fed from the plate circuit of a triode and 1n addition the combination of the feature of neutralization.

This invention relates to the use of the audion as an amplifier with thedeliberate l5 elimination of regeneration and combinatlon circuit oscillations.

Inthe use of the audion as an amplifier, it is desirable to limit the oscillation from the signal to be amplified to the so-called grid or input circuit of the audion and so far as this audion is concerned it is desirable to limit the amplified oscillation in the plate circuit to the plate circuit itself. It has been discovered, however, that in addition to the electric connection through the stream of electrons flowing from filament to the plate there is, especially for high frequency oscillations, the equivalent of a connection between the plate and the grid of the audion due to the capacity between these contiguous elements.

To be sure, this capacity is minute, but it becomes appreciable for oscillations of high frequency. Thus, without some suitable provision, instead of having two separate and distinct circuits terminating respectively in the filament and the grid and in the filament and the plate, we have a third combination circuit oscillating through the major portions of the grid and the plate circuits in seri'es and across the capacity between the plate and the grid.

I propose to carry to the. grid a reverse feed back coupling effective in applying to it directly an 180 displaced A. C. potential equal to that tending to drive the undesired oscillation. What is necessary to be done is to find in the ordinary hook up of a multistage audion amplifying system a locality wherethe alternating potential is 180 out of phase with the potential V. This is true for the secondary coil of each transformer between the stages of audion amplification. Having located this source of out-of-phase alternating potential, its value will be A V.

v to that of the undesired tendency.

By feeding it back to the grid, through a regulating condenser G I have a connection opposite in its effect to the instrumentalities tending to set up the undesired oscillation in the combination circuit heretofore mentioned. But more than this is desired. It is necessary that the tendency of this neutralizing circuit to set up oscillations be exactly the same in value although opposite in sign The above will all be better understood by reference to the illustrative embodiments of the invention to which the, claims are directed merely for purposes of illustration and not limitation. These illustrative embodiments are described in the following specification in'connection with. the accompanying drawings which form part hereof and in which like characters designate correspondin parts in the figures.

In the rawings,

Fig. 1 is a diagrammatic representation of one layout of an amplifying receiving set for the reception, amplification and detection of radio signals;

Fig. 2 is a similar diagram showing a modification; and

Fig. 3 is a diagram illustrating the principle of neutralization directly at the grid.

In the embodiments illustrated 1, 2 and 3are suitable radio transformers preferably each comprising a primary coil 4 and a secondary coil 5 of any suitable ratio such as 1 to 3, the preferred construction being two cylindrical helices, a primary 4 located within and close to the secondary 5, such as described in my co-pending application, Ser. No. 737,097, filed September 11th, 1924, for coupling coil and process of making same. 7, 8 and 9 are variable condensers of a capacity in a-range of adjustment to tune the associated'secondary coil to the frequency of the desired signal throughout the desired wave band for which the set is adapted. 11, 12 and 13 are suitable electric amplifying devices containing each an input electrode called a grid, an output electrode called a plate and a common electron emitting electrode called the filament or cathode, the whole designated commonly as an audion.

A is the A battery for heating the filament and B is the usual 13 battery; T the telephone receivers. 15 and 16 are adjustable minute neutralizing condensers.

The electric disturbance picked up by the no antenna 17 oscillates from the antenna 17 to the ground 18 through the primary coil 4 of transformer 1. An adjustment of variable feature for the tuning or selectivity feature of this invention. This circuit may be traced as follows: source 20, lead 21, ground wire 22, lead 23, filament F, grid G, lead 24,

.lead 25, back to source 19. The plate circuit for this audion 11 may be traced as follows:

-.B battery B, ground wire 22, filament F, plate P, lead 26, primary 4 of transformer 2, lead 27, line wire 28', back to battery B. It has been found. however, that, especially for high frequency, the effective circuits for such an audion amplifier are not quite so simple. For example, there is inherent capacity C, indicated in dotted lines in the figures between the grid G and the plate P, so that in reality for the audion 11, in addition to the grid and plate circuits tracel, there is a second combination circuit including the grid and plate circuits previously traced (except for the lead 23 and filament F) in series across the condenser C. Thus, oscillations set up in the grid circuit of audion 11; or any part thereof, may oscillate through this combination circuit to the detriment of the sig nal desired to be received. I directly neutralize this combination circuit by employing another-pr feed-back potential wave and applying to the grid G directly an electromotive force wave 6 equal and opposite, that is, equal to, but out of phase 180 with the electromotive force wave 6 theoretically applied to the grid G of audion 11 tending to effect the oscillations in the aforementioned combination circuit (see Fig. 3). My preferred method of accomplishing this result is to utilize the electromotive force wave of the secondary coil 5 of transformer 2, which is coupled with the primary coil 4 of this transformer. It should be noted that this transformer too like all the radio transformers is of the air core type incapable of giving unity coupling from primary to secondary and cooperating for selectivity as an iron core transformer cannot do. Energy loss from pimary coil to secondary coil is desired. This electromotive force wave is 180 displaced from that tending to produce coupling between the grid and the plate of audion 11 by reason of the reversed terminals shown. Any suitable point on the secondary coil/ 5, separated from the ground terminal 30, the desired number of turns to produce the desired electromotive force, is

selected. In Fig. 1. the opposite terminal 31 is employed. This is connected back by lead 32 to the adjustable condenser 5, thence by lead directly to the grid G.

In the diagram illustrated, the audion 13 is used preferably as a detector in which the tuned circuit from the transformer secondary 5 is connected between the filament F and the grid G of audion 13, preferably through the grid condenser 10 and grid lead 11. The telephones T may be connected directly in the plate circuit of audion 1?, as illustrated or furtherstages of amplical'ion may be employed. as desired.

What I most desire to emphasize is that no additional apparatus such as an auxiliary coil is introduced into or involved with any of the grid'circuits or, for that matter, no auxiliary coils whatsoever are employed. My primary object is to select and en'ipl'oy what may be termed a counter-altemating electromotive force and apply it directly to each grid that I desire to neutralize. so that the effect of capacity coupling between the grid and plate is annulled. In carrying this out, I use the secondary potential of the amplifying transformers necessary themselves for amplifying purposes in the receiving set to furnish this neutralizing electromotive force, which transformers themselves are of the type to effect selectivity. I employ no connection whatsoever with the plate of the audion to effect this neutralization. For purposes of neutralization, the alternating potential on the plate lead will be in phase of the alternating electromotive force tending to produce the undesired coupling, and did I wish to use such a connection, I would require an electromagnetic linkage of an auxiliary character with the grid to obtain the necessary phase displaccment; but in carrying out my invention it is precisely this which I desire to avoid and do so by the utilization of an already existent electromotive force wave of the desired 180 displacement to effect my neutralization. In the figures are shown the only special connection requirements, namely, that for each transformer 2 and 3 primary and secondary coil terminals of unlike electro-magnetic polarity lead to the cathode connection.

The inventive thought may have a variety of expressions as is contemplated by what I claim and desire to secure by United States Letters Patent as follows:

1. A sharply selective, radio-frequency amplifying receiver comprising a triode having a grid, a plate and a cathode; means for applying radio frequency waves across said grid and cathode; a radio frequency transformer of the air core type comprising a primary coil of a few turns and a spaced secondary coil of more turns coupled to said primary 'coil so that substantially sharp, independent tuning of said second,

ary coil may be effected; a variable condenser for tuning said secondary coil; an amplifying source of direct current energy; circuitconnections from said plate through said primar coil and. said source to said cathode an from such terminal of said secondary coil to said cathode that coil terminals of unlike electro-magnetic polarity lead to said cathode; and a reverse feed back coupling substantially to neutralize the grid and plate feed back coupling associated with said triode comprising a limiting condenser of suitable 'low' capacity, a

tap-off from' a suitable potential point on said secondary coil to said limiting condenser. and a connection to said grid from said limiting condenser; Y

2. The receiver as defined in claim 1 and further characterized bythe following that a I second similar triode has connections across its grid and cathode from the terminals of saidsecondary coil whereby said second triode is -rcsponsive substantially only to the wave energy transferred from,

said primary coil to said secondary coil; a

second similar air-core radio frequency transformer with its primary coil energized from the plate of said second triode and said source of direct current energy; terminals of unlike polarity of the rimary and secondary coils of said secon transformer being connected to the cathode of said second triode; a second variable condenser connected across the terminals of the secondary coil of said second transformer for selective tuning substantially independently;,and a second reverse feed back coupling substantially to neutralize the grid and plate feed back coupling associated with said second triode comprising a limiting condenser of suitable low capacity, a tap-ofi from a suitable potential point on said secondary coil to said limiting condenser and a connection to the grid of said second triode from said limiting condenser.

CARL o. WEBER. 

